DE69900536T2 - Detection and rejection of forgery of two-sided documents - Google Patents

Description

The present invention relates to an apparatus and method for deterring the counterfeiting of two-sided documents and, more particularly, to preventing the printing of counterfeit money and other counterfeit documents.

Modern technology makes it easy, quick and inexpensive for most people to make exact color copies of documents. This copying can be accomplished by using a color copier or by scanning the document and then printing it using a color printer. There are many legitimate uses for this copying technology. However, a small percentage of people use color copying to make counterfeit money or forge other documents.

One way to prevent counterfeiting is to use techniques such as those taught by Sato in "Color image input apparatus having color image identifying function," United States Patent 5,638,496, issued June 10, 1997. Sato describes a line sensor and an image input section that input a color image into a reading area containing an original, an original extraction section that extracts a region of the original from the input image, a normalization section that normalizes an image of the extracted original region into an image of predetermined size, an image averaging section that converts the normalized image into an averaged image, and a brightness-hue-chroma conversion section that converts the averaged image into Vcd images that are used as human color perception levels. A structure matching section compares the Vcd image with directory data in a directory data storage section to determine whether or not the original is a certain type of original such as a bill, and an image output control section then determines whether or not an image data output should be output from the color image input section to the outside based on the result of the identification.

For example, typical techniques such as looking for a particular pattern or color distribution can be used to detect and stop the copying of counterfeit documents. However, these techniques can be computationally intensive and therefore introduce an undesirable delay in copying each document. This delay is particularly undesirable when one realizes that the majority of copied documents are not produced by counterfeiters but by law-abiding citizens copying documents for legitimate purposes.

It is thus evident that current counterfeit detection and deterrence methods result in processing delays in color copiers and prevent the use of these devices in many applications.

Therefore, there is an unresolved need for a counterfeit detection and deterrence method that enables color copies to be made without causing processing delays in color copying machines.

Another method is known from US-A-5629770, which is intended to prevent the illegal copying of electronically published documents. It involves publishing a plurality of copies of electronically generated material to be distributed to a plurality of subscribers. Each copy of a subscriber's document has a unique identification code embedded in the document. The arrangement of the code on the document is based on the line shift and word shift techniques. This is intended to minimize the effects of noise and distortion on future illegal copies in order to facilitate detection and decoding of the unique code. A codebook is created to assign each unique code to a subscriber.

Another method and apparatus for detecting and deterring counterfeiting is described which enables legitimate copies to be made without introducing significant visual artifacts or causing significant processing delays. It is possible to include a matching pair of alignment indicia opposite each other on opposite sides of a two-sided security document which is often counterfeited. The present invention causes a small, random offset or jitter in the position on a side where printing of a copy of a document will begin. The jitter makes it very unlikely at that point that the alignment indicia will align when the security document is copied. The misalignment of the indicia signals that the copy is a counterfeit.

For one embodiment, dithering is always introduced. Alternatively, dithering is only introduced if forgery is possible or likely.

This invention has a negligible impact on the time to render a page and a negligible effect on general images and documents, while producing easily identifiable artifacts on counterfeit copies of two-sided security documents. This scheme can be applied in a printer driver without hardware changes, and the conditions that determine when the jitter is introduced can be fine-tuned so that the circumstances considered suspect can be adjusted to achieve a compromise that allows adequate detection while producing only a minimal effect on legitimate users:

The invention will be readily understood from the following detailed description taken in conjunction with the accompanying drawings, in which like reference numerals indicate like structural elements.

Figure 1 is a diagram illustrating a color copying system suitable for use with a counterfeit detection and deterrence scheme according to the present invention.

Fig. 2 is a diagram illustrating a process flow according to an embodiment of the present invention.

Figure 3 is a diagram illustrating a pressure offset introduced according to an embodiment of the present invention.

Fig. 4 is a diagram illustrating a first alignment icon according to an embodiment of the present invention.

Figure 5 is a diagram illustrating a second alignment icon suitable for use with the first alignment icon of Figure 1, according to an embodiment of the present invention.

Figure 6 is a diagram illustrating the alignment of the alignment icons of Figures 4 and 5 when properly aligned, according to an embodiment of the present invention.

Figure 7 is a diagram illustrating the misalignment of the alignment icons of Figures 4 and 5 when there is a horizontal offset, according to an embodiment of the present invention.

Figure 8 is a diagram illustrating the misalignment of the alignment icons of Figures 4 and 5 when there is a vertical offset, according to an embodiment of the present invention.

Figure 9 is a diagram illustrating the misalignment of the alignment icons of Figures 4 and 5 when there is both horizontal and vertical offset according to an embodiment of the present invention.

Embodiments of the invention are explained below with reference to Figures 1 to 9. It will be apparent to those skilled in the art that the detailed description given herein with reference to these figures is for explanatory purposes only, since the invention extends beyond these limiting embodiments.

When a two-sided document that is to be protected against counterfeiting has features that are highly dependent on exact alignment of the front and back of the document, accurate alignment becomes very important to the counterfeiter when printing a copy. Here, a simple scheme is proposed that makes it difficult for counterfeiters to achieve absolute alignment.

Fig. 1 is a diagram illustrating a color copying system suitable for use in a counterfeit detection and deterrence scheme in accordance with the present invention. An image capture device 120 captures an image of an original document 110. An image processor 130 processes the image captured by the image capture device 120 so that a printer 140 can produce a copied document 150. As will be explained in detail below, the image processor 130 has the ability to insert a random offset, or dither, into the captured image of the original document 110. If the document to be printed is a two-sided document, the registration icon (one on each side), the image processor 130 forces a misalignment of the image characters when the printer 140 produces the copied document 150. The misalignment caused by the jitter thus identifies a copy as a counterfeit.

Certain documents, such as banknotes, have security features that require very precise alignment of the front and back of the note. One example is the Portuguese 1000 escudos note. A section of a cross is printed on the front and the rest on the back. When the note is held up to a light source, the entire cross becomes visible, making any misalignment of the two halves obvious. If a counterfeiter wants to produce a good imitation of such a note, he must align the front and back very precisely. This is very difficult to achieve with a cheap printer or copier that requires reloading the paper to print the second side. However, with care, a counterfeiter may be able to achieve a sufficiently precise alignment to defeat such a feature.

For one embodiment of the present invention, before beginning rendering, a component of the image processor 130 (such as the printer driver) adds a random vertical and horizontal offset from the point on the page (typically the upper left corner) where the process would begin. Thus, if the printer would normally begin rendering at a location at an offset (x, y) from the physical page corner, it will instead begin printing at (x + R, y + S), where R and S are random offset factors. For example, if R and S were uniformly allocated in the range (- 1/16, 1/16) inches, a resolution of 600 dpi would result in a random jitter of 75 dots in each direction. This would mean, in the worst case, a 1/16 inch offset from the desired margin values. If R and S are chosen independently for each page reproduced, this would mean that the probability that a forger would achieve perfect alignment when the second page of a document is printed is 75⁻² (about 0.000178).

A banknote, such as the Portuguese 1000 escudos banknote, is an example of a security document that has alignment icons. Other examples of two-sided documents that have a matching pair of alignment icons and that may be targets of counterfeiters include: identity cards, securities, or stock certificates. It is noted that in some cases the only thing printed on one side of a document may be an alignment icon that matches an icon on the other side of the document. It is also noted that it is possible for the icon to be integrated into the document so that it would not be noticed unless one were to look for it. In fact, it is possible for one side of the document to be a mirror image of the other side. Although the security document will usually have at least one color, this is not necessarily the case. The scheme presented here also works to protect black and white or grayscale documents.

The image capture device 120, the image processor 130 and the printer 140 may, as shown in Fig. 1, be separate components. The image capture device 120 may be a scanner or a digital camera, but it may also include a device that graphically produces the "captured" image. The image processor 120 may be a dedicated computer or a general purpose computer, where the image processing function may be accomplished by software (e.g., as a printer driver), by hardware, or by firmware. The printer 140 may operate on a variety of known printing methods using mechanisms such as toner or ink. Alternatively, one or more of these components may be combined, e.g., as an integrated color copier that scans, processes, and then prints. It is noted that it is possible for the image processing function 130 to be distributed throughout the system. Thus, a portion of the image processing function 130, or even the entire function, may be accomplished by the image capture device 120 or the printer 140.

Fig. 2 is a diagram illustrating a process flow according to an embodiment of the present invention. The interesting portion of the image processing begins at a start bubble 210. At a decision block 220, a test is made to determine whether or not counterfeiting of a security document is possible. For example, if it is known that the document to be printed is to be printed as a black and white or gray scale copy, it is not possible to produce a counterfeit copy of a document having a particular color. This is due to the fact that the copy does not have the particular color, so there would be no opportunity to confuse the non-colored copy with an original. Therefore, in a case just described, to save processing time and avoid misalignment of two-sided documents under safe printing conditions, there is no need to introduce jitter. It is noted that test 220 is optional and could be omitted, the only significant effect being that a small amount of jitter would occur in any case with an associated increase in processing delay.

At decision block 230, a test is made to determine if the user has specified an "exact" print mode. If an exact mode was specified, e.g., by selecting a print option when printing or copying, decision 240 would perform a test to determine whether or not the document to be printed was printed under suspicious circumstances that would indicate the likelihood that a counterfeit copy of a security document was made. If exact mode was specified and no suspicious circumstances were detected, this portion of processing would end at end bubble 270 without introducing a jitter. On the other hand, if a suspicious circumstance were detected, an offset (block 250) would be calculated and then the page to be printed adjusted by applying the offset (block 260).

Again, it is noted that test 230 is optional and could be omitted, the only significant effect being that a small jitter would occur in any case with an associated increase in processing delay.

The advantage of enabling exact mode is that it would allow the user to make accurate copies with front-to-back alignment in the event that a backup copy is unlikely to be tampered with. For the majority of users, the introduction of a small jitter would not be a problem and would not use exact mode when printing. This would allow printing without an associated processing delay associated with detecting suspicious circumstances that would indicate a likelihood of tampering.

Depending on how wide a net is to be cast, one or more tests known to those skilled in the art could be performed to detect suspicious circumstances. One example of a suspicious circumstance that could be detected is a recent history of printing a significant amount of a particular color, such as the "bill green" found on the back of U.S. currency. Another example would be to test the image of the document being printed for the presence of an identifying artifact. This identifying of artifacts could include the presence of a distinctive color or the presence of a distinctive feature, such as a president's face, a treasury seal, or even the alignment icon itself.

An example of a scheme that allows for rapid identification of the use of a particular color is described in a separate patent application by C. Herley and X. Yang, "Detection and Deterrence of Counterfeiting of Documents having a Characteristic Color," filed on the same date as the present invention. Using this approach, the number of times a region of a color lookup table corresponding to the particular color is accessed can be counted, e.g., when pixel values are converted from the RGB color space of a captured image to the CMGK color space used to print the image. Although general images may contain small amounts of a particular color, a suspicious circumstance could be detected when a threshold number of pixels access the region of the lookup table associated with the particular color.

Note that in the simplest case, decision blocks 220, 230 and 240 would be eliminated. An offset would simply be calculated (block 250) and then the page to be printed adjusted by applying the offset (block 260). For this embodiment, the offset would be applied without restriction to all documents to be printed.

Figure 3 is a diagram illustrating an introduced print offset according to an embodiment of the present invention. In Figure 3, the crosshairs indicate the position on a page 310 where printing of a print area 320 would normally begin. The arrow from the center of the crosshairs to the upper left corner of the print area 320 indicates the offset that has been introduced.

Figures 4 and 5 are diagrams illustrating examples of first and second alignment icons that together form a mating pair, according to an embodiment of the present invention.

This means that an icon 400 of Figure 4 may be included on a first page of a document, with an icon 500 of Figure 5 included on the other side of the document directly opposite the icon 400. Figure 6 is a diagram illustrating the structure 600 formed by the alignment of the alignment icons of Figures 4 and 5 when properly aligned, according to one embodiment of the present invention.

Figure 7 is a diagram illustrating the misalignment of the alignment icons 400 and 500 (of Figures 4 and 5, respectively) when there is a horizontal offset "R" according to an embodiment of the present invention.

Similarly, Fig. 8 is a diagram illustrating the misalignment of the alignment icons when there is a vertical offset "S", and Fig. 9 is a diagram illustrating the misalignment of the alignment icons when there is both a horizontal and a vertical offset.

It should be obvious that the same alignment icons can be applied to an entire page, or that different icons can be applied to different parts of a page. Similarly, it should be obvious that the introduction of dither can be applied to an entire page, or that different dither can be applied to different parts of a page.

In summary, the advantages of the presented random dither introduction scheme include the following:

- Virtually no impact on the time it takes to render a page.

- Imperceptible impact on the desired margins of a page to be printed, while making absolute alignment difficult.

- Minimal change to the driver software, which may include, for example, only the generation of one or two random numbers per page.

- Normal users will probably not even suspect that a security feature has been used.

- It is possible to "upgrade" the installed base of printers because drivers are usually updated with operating system updates.

The many features and advantages of the invention will be apparent from the written description, and the appended claims are intended to cover all such features and advantages of the invention.

Claims (10)

1. A device for deterring the forgery of a two-sided security document having a matching pair of alignment symbols, the device being characterized by the following features: an offset generator adapted to obtain a random offset for a captured image to be printed; and a shifter adapted to apply the random offset to a printed area of a page of a document to be printed, the printed area corresponding to the captured image, the random offset resulting in an unpredictable misalignment of a first alignment icon of the matching pair captured from a first page of the document to be printed with respect to a second icon of the matching pair captured from a second page of the document to be printed. 2. The device of claim 1, wherein the offset is a horizontal offset, a vertical offset, or both a horizontal and a vertical offset. 3. Apparatus according to claim 1 or 2, comprising a suspicious activity detector adapted to determine whether a particular page to be printed is to be printed under suspicious circumstances encountered in forging a security document, and to apply the offset only when the suspicious circumstances are detected. 4. Apparatus according to any preceding claim, comprising a feasibility detector adapted to determine whether a particular page to be printed should be printed in a manner that is possible to print the security document, and to apply the offset only if it is possible to print the security document. 5. Apparatus according to any preceding claim, comprising a printer (140) adapted to print the page to be printed. 6. Apparatus according to any preceding claim, comprising a detection device (120) adapted to detect the image of the document to be printed. 7. A method for deterring counterfeiting of a two-sided security document having a matching pair of alignment indicia, the method being characterized by the steps of: Obtaining a random offset for a captured image to be printed; and Applying the random offset to a printed area of a page of a document to be printed, the printed area corresponding to the captured image, the random offset resulting in an unpredictable misalignment of a first alignment icon of the matching pair captured from a first page of the document to be printed with respect to a second icon of the matching pair captured from a second page of the document to be printed. 8. The method of claim 7, wherein the offset is a horizontal offset, a vertical offset, or both a horizontal offset and a vertical offset. 9. A method according to claim 7 or 8, comprising the following steps: Determining whether a particular page to be printed is to be printed under suspicious circumstances that exist when the security document is forged; and Apply the offset only when the suspicious circumstances are detected. 10. A method according to any one of claims 7 to 9, comprising the following steps: Determining whether a particular page to be printed should be printed in a manner that is possible to print the security document; and Apply the offset only if it is possible to print the security document.